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Martian tracks Getting bogged in a sand trap while driving off road can ruin your day on planet Earth, but as NASA's rover Spirit discovered, doing it on Mars can be fatal.

In May 2009, the golf-cart sized rover cracked through a crusty layer of Martian top soil and sunk into softer underlying sand, becoming permanently trapped.

Despite months of remote manoeuvring attempts, Spirit was never liberated, and eventually shut down.

Spirit's twin rover Opportunity is continuing to explore the red planet, and a year ago the larger more advanced Curiosity rover also arrived on Mars.

To ensure these, and future rovers don't become bogged, Dr Carmine Senatore of the Massachusetts Institute of Technology and colleagues, have developed a new computer model called Artemis, which can accurately simulate how a rover will respond in differing Martian soils and terrain.

"It looks like a computer game, but gives us the opportunity to understand how the rover moves and how it performs on soft materials," says Senatore.

Mission managers using a combination of sensors aboard the rover, and satellite observations from orbit, can analyse the terrain along the rover's planned path, which can then be analysed by Artemis.

"It can help us plan routes ahead of time and simulate different options," says Senatore.

"We can try them in the simulator rather than in the real world, so we can predict how the rover will perform, if we're going to get stuck or if it's safe to drive through there."

Different world

Mars has only a third the gravity of Earth, which means soils act differently on the red planet than they do back home.

"The sand on Mars tends to bear less load than you would expect on Earth," says Senatore.

"So when the material is loose up there, it tends to be looser than the counterpart here on Earth, and tends to limit the performance of the vehicles, so that's a big challenge for mobility."

The new Artemis simulation is designed to deal with these differences better than previous models.

Researchers initially tested Artemis on a duplicate of the Opportunity Rover at the JPL Mars yard, an Earth bound copy of the Martian environment, and are now focusing on the larger Curiosity rover.

A report to be published in the Journal of Field Robotics found the Artemis simulations behaved much like the real rovers on Mars.

Hard road ahead

Artemis will be crucial as Curiosity begins its primary mission, a journey across the Gale Crater impact basin.

So far, mission managers have tended to steer the rover over relatively benign terrain, consisting of mostly flat, firm surfaces.

However, Curiosity is expected to encounter more challenging conditions as it treks towards its ultimate target, the five kilometre high central peak called Mount Sharp-

"One of the big challenges will be to climb steep inclines and that's where this tool will be extremely beneficial," says Senatore.

"It will give us the possibility to test in simulation, different scenarios and estimate the risks of different alternatives."